Fuse link



R. H. EARLE pril 28, 1942.

FUSE LINK Filed Feb. 26, 1940 INSULATION INVENTOR.

ATTORNEY.

Patented Apr. 28, 1942 r FUSE LINK Ralph nl Earle, wauwatosa. wis.,animar to Llnc Materia l Company, Milwaukee, Wis.. a ycoa'potation ofADelaware Application February ze, 1940, serial No. 320,903

(c1. zoo- 135) 17 Claims.

This invention relates to improvements in fuse links.

It is desirable to provide for a pretensioned I fractional amperage fusellnkadapted for use in electrical distribution systems, a fusiblesection that will rupture ons. small fault current in a relatively shortperiod of time, which will not blow unnecessarily on lightning surgesand which is strong `mechanically. These requirements prevent the use ofthe type of fusible section, such as illustrated in the pendingapplication of Alwin G. Steinmayer and Chester W. Brown, Serial No.199,335, filed April l, 1938, for Pretensioned fuse link, heretofore incommon use, because it has been impractical to make fusible sections ofthis type\suilic iently small to render them operable on fractionalampere currents, and at the same time strong enough mechanically towithstand the constant mechanical strain commonly occuring in apparatusof this type. In other words, if the diameter of the strain wire issufilciently small to function properly on a small fault current, itwill be too weak mechanically to withstand the mechanical strainandconsequently rupture unnecessarily.

Therefore, it is an object toprovide a fuse link having a strain sectionincluding a meltable portion, a major part of which is not subjected tothe direct flow of current but is subjected to the influence of heatgenerated by the ilow of current through the link, thereby permittingthe strain section to rupture upon the occurrence of a predeterminedcurrent and thereby introduce a gap in the circuit.

Another object of this invention is to provide in a fuselinkcomprising aconducting member, a strain section insulated from the conducting memberand including a meltable joint in combination with an electricallyconductive heat-generating portion which bridges the insulated end ofthe strain section and subjects the joint to heat sufficient to permitrupture thereof upon the occurrence of a predetermined current flowthrough the link.

Also, another object is to provide in a fuse link, a heat-destructiblemechanical Joint in combination with an electrically-conductiveheat-producing means which is out of mechanical contact with one part ofthe joint, thereby permitting free separation of one part of the jointfrom the heatproducing'means upon the occurrence of a predetermined fiowof current through the link.

It is also an object of this invention to provide for a pretensionedfuse link having a fusible section comprising current-conductingportions electrically and mechanically joined by a lowmelting pointalloy, a heater winding of resistance wire adapted to melt the alloy andallow separation of the electrically-conductive portions upon theoccurrence of a predetermined current. r Still another object is toprovide for a pretensioned fuse link having a fusible section comprisingcurrent-conducting strain wires electrically and mechanically joined bya low-melting point alloy, a heater winding of wire having a greatercurrent-carrying capacity than the strain wires, whereby the strainwires will melt on a heavy short circuit before the soldered joint hasparted, thereby introducing a gap in the circuit.

A further object is to provide for a pretensioned fuse link having afusible section comprising current-conducting strain wires electricallyand mechanically joined by a low-melting point alloy, a heater windingof wire having a greater current-carrying capacity than the strainwires, whereby the strain wires will melt on a heavy short circuitbefore the heater winding itself has been rendered inoperable.

A further object is to provide for a fuse link a pair of fusiblesections, one of which includes a heat-responsive means and anelectrically-conductive heater winding in series relationship with theother of the fusible sections, whereby the heater winding acts to meltthe heat-responsive means upon the occurrence of a moderate overload,whereas upon the occurrence of a heavy short circuit the other of thefusible sections is rupturedI either section operating to introduce agap in the circuit.

A further object is to provide for a fuse link a pair of fusiblesections, one of which includes a heat-responsive means; an insulatingelement and an electrically-conductive heater winding bridging theinsulating element and being in series relationship with the other ofthe fusible sections, the heater winding acting under moderate overloadto melt the heat-responsive means, whereas upon the occurrence of aheavy short circuit the other of the fusible sections is .rup-

tured, either section operating to introduce a gap in the circuit.

A still further object is to provide in a fuse link having adestructible mechanical Joint including a heat-conducting portion and anelectrical conductor connected by a low-melting point alloy, acurrent-conducting heater coil adjacent the heat-conducting portion, thehea r coil operating to generate sumcient heat at a'rfietermined currentvalue to melt the alloy and ereby Dermit the joint. when placed undertension, to be ruptured. Y

Still another object is to provide for liquid fuses a fuse link having astrain section comprising a pair of cooperating sleeves joined by` alow-melting point alloy and a heater winding of high resistance wiredisposed within at least one of the sleeves for conducting an electriccurrent and adapted to generate heat at a predetermined current valuesufilcient to melt the alloy and permit separation of the sleeves whenplaced under tension, thereby interrupting a circuit through the link.

Also an object is to provide in fuse links, a mechanical joint includinga heat-responsive means in combination with a heater coil which iselectrically associated in series relationship with the joint andrelatively positioned thereto, whereby heat from the coil uponapredetermined current flow through the link will destroy the means andpermit separation of the joint when placed under tension, therebylinterrupting the circuit through the link.

In the drawing:

Fig. 1 is a view in side elevation, partly in section, showing aspring-tensioned fuse link embodying one form of this invention.

Fig. 1A is an enlarged view of the intermediate portion of the fuse linkshown in Fig. 1. A

Fig. 2 is a view in side elevation, partly in section, illustrating amodification of this invention.

Fig. 3 is a sectional enlarged view taken on the line 3-3 of Fig. 2.

Fig. 4 is a fragmentary sectional view taken on the line 4-4 of Fig. 3.y

Fig. 5 is a View in side elevation of a liquid fuse showing a furtherembodiment of this invention, parts of the structure being broken away.

The fuse link shown in Fig. 1 comprises a contact button I, a rigidterminal 2 formed of tubular stock to provide a flattened portion 3having a notch at 4 adjacent its upper end and a threaded tubularportion at 5 adjacent its lower end. When the terminal is thus formed,shoulders 6 are provided intermediate the ilattened and threaded portionof the terminal 2 by the flattening of the portion 3.

An insulating tube I made of fibre or any similar electricallynon-conductive material is threadedly mounted on the threaded portion 5and supports a strain section 8 at its lower end in non-conductingrelationship with the rigid terminal 2.

' its upper end by a tubular insulator 25 surroundterminal 2, coiled at2| about the reduced portion II on the tube 9 and secured at its lowerend to the portion II at 22. The resistance wire 20 has a greatercurrent-carrying capacity than the strain wire I2 for reasonshereinafter described. Interposed between the coil 2| and the tubularportion II is a mica sheet 23 or similar heat-resisting insulatingmaterial for holding the coil out of direct contact with the portion II.As will be seen from the drawing, the upper portion of the resistancewire 20 passes downwardly through the tube 'I and to the exterior of thetube 9 through the aperture I3 and is held in insulated relationtherewith by means of an insulating sleeve 20A. Mounted upon theconductor I5 is a coil spring 2 4 which is spaced therefrom at ing thestrain wire I2 and anchored thereon by means of the reduced convolutions26. The lower end of the spring 24 is provided with a ferrule 21threaded thereon for engagement with the lower end of an insulating tube28 which surrounds the spring 24, strain section 8, and tube l. Theupper end of the tube 28 is provided with a collar or washer 29 whichengages the shoulders 6 on the terminal 2. l y

The insulating fuse tube 28 is mounted upon the fuse link Vbefore theterminal 2 is flattened and threadedly engaged with the member I. Thespring 24 is expanded as the ferrule 21 is forced downwardly by thelower end of the tube 28. The top of the tube 28 is positioned (duringthe assembly operation not shown) a short distance below the top of thememberI in order to expose enough of the member to permit it to be rmlyheld Yas the terminal 2 is threaded into place and flattened asheretofore described. After the The' strain section 8, more clearlyshown in Fig. 1A, comprises a metal tube 9 threaded at III forengagement with the member I and having a' reduced portion II extendingdownwardly a short distance from the threaded portion III, a strain wireI2 extending into the portion II to a point below the aperture I3 in theportion II, and a low-melting point heat-responsive alloy I4 whichsecures the wire I2 to the portion II. It may beg'noted that theheat-responsive alloy I4 may, fr example, comprise a mixture of bismuthand 40% tin. v

The strain Wire I2 extends into a rigid tubular conductor I5 and issecured therein by means of an indent I6 in the conductor I5. Theconductor I5 is secured to a flexible leader I'I by means of a deformedferrule I9.

`Mounted on the reduced portion II of the tube 9, is a predeterminedlength of -high resistance wire 20 which is secured at its upper end tothe member 2 is flattened and the tube 28 is released,

the spring 24 urges the tube into abutting relay 30 of the wire I2 fromthe tube 9 normally held i therein by the alloy I 4.

Normally the fuse link operates to conduct an electric current by meansof the terminal 2, the heater coil 2|, the lower end of the tube 9 andalloy I4, the strain wire I2 and the conductors I 5 and I'I. Heatgenerated by the heater coil is directly proportional to the resistanceof the wire 20 and the square of the current flowing therethrough.Therefore, it may be seen that the amount of heat. produced by means ofthe heater coil conducting a predetermined amount of current, isregulated by the length, size and kind of wire used.

Under normal load currents which the link is` designed to conduct, theheat generated by the* has been ruptured by a heavy short circuit, itsruptured ends'are drawn apart by means of the spring 24. therebyintroducing a gap in the circuit.

Figs. 2, 3, and 4 show a modification of the fusible section, previouslydescribed, including a terminal 3| flattened at 32 to hold a strain wire33 therein and to form shoulders 34 'against which a collar 35 isanchored.

The lap joint fusible section 36, more clearly shown in Fig. 4 and asmore fully disclosed in the pending application hereinbefore referredto, comprises a foil-like metal strip 31 having each end arcuately benttoward each other at 31A and provided with apertures \,36 through eachAof which the strain wire 33 extends. A strain wire 33 bent doubleisinserted through the lower aperture 33 so that its upper ends 46 extendthrough the upper aperture 36. The strain wires are held againstseparation from each other by a low-melting point alloy 4l lying betweenthe arcuately-bent ends 31A of the metal strip 31.

A strain wire v42 extending upwardly from the conductor l is tensionedand anchored in the manner described heretofore with reference to Fig. 1and is connected to and insulated from the lower end of the strain wire33 by means of an insulating block 43 which is provided at each end withapertures 44 receiving therein the respective strain wires 33 and 42 asindicated. It may be noted that the block 43 connects the fusiblesection 36 in non-conducting relation to the conductor 42. A heater coil45 comprising a predetermined length of high resistance wire 20A,provided with a covering of insulating material such as enamel 45A, isconnected at the upper end of the metal strip 31 by any convenient meansas solder 46 and extends downwardly around the alloy and metal strip ina series of spaced apart convolutions 41 each being insulated from theother and from the strip and alloy by the enamel 45A or similar materialnot readily carbonized by heat. The lower convolution extends downwardly into a length of wire 46 which is secured to the strain wire 42at 43A below the insulating block 43. It may be noted that theresistance wire 26A and the strain wire42 have a greatercurrent-carrying capacity than the strain wire 33 for reasonshereinafter apparent.

The fuse tube 28 is mounted over the fusible section 36 and in relationto the spring -24 in the manner heretofore described in reference toFig. 1.

The link shown in Fig. 2 functions electrically in the manner heretoforedescribed with reference to Fig. l, the current being conducted throughthe link by the terminal 3l, the strain wire 33, the heater coil `45,the strain wire 42 and the conductor I5. Under normal operatingconditions the heat generated by the heater coll 45 is not sumcient tomelt the alloy 4i.- When a moderate overload current occurs, the heatercoil 45 generates heat sumcient to melt the alloy 4l and thereby allowthe entire lower portion of the link to be withdrawn from the strainwire 33 and interrupt the flow of current through the circuit to whichthe link is connected. When a heavy short circuit occurs, the lessercurrentcarrying capacity strain wire 33 melts before the greatercurrent-carrying capacity strain wire 42 has melted or the heater coil45 has allowed section 36 to function. Under ruptured conditions, thespring 24 operates to introduce a gap in the circuit in a mannerdescribed in reference io Fig. 1.

Fig. 5 illustrates a well-known type of liquid fuse 49 which comprisesan insulating tube 56 of glass or other suitable material provided witha lower contact 5I and an upper contact 52. The upper contact 52 isprovided with shoulders 53 against which a bridge member 54 issupported. A conducting member 55 which operates as a fusible sectionunder predetermined conditions of short circuit is attached to thebridge in any suitable way, as by means of a bolt 56.

The fuse link designated generally by the numeral 51 comprises a metalsleeve 58 spun inwardly at. 59 to form a support against which aninsulating disk 60 is anchored. The lower end of the conducting member55 extends through the apertures 6| in the disk and isheld therein bythe loopedend 62. The lower portion of the sleeve 56 encircles the upperportion of a cup-like conducting member 63 spaced therefrom by a narrowmargin, the sleeve and member being held in rigid relation to each otherby a lowmelting point alloy 64 disposed within the margin as shown. Itmay be noted that the insulating disk 60 holds the fuse link 51 innon-conducting relation to the conducting member 55.

A heater coil 65 comprising a series of convolu tions mounted upon aninsulator rod 66, made preferably of a ceramic material and furtheridentified by the word Insulation, is disposed within the cup member 63and secured therein by an electrically non-conductive cernentitiousmaterial 61` The coil is formed of a predetermined length of highresistance wire, preferably of the kind described in reference to Fig.l. The upper end of the coil is joined to the loop 62 by any convenientmeans as by solder 66 and the lower end extends through the aperture 69in the bot tom of the cup 63 where it is electrically secured in anysuitable manner, not shown. A heatin sulating material, such as cork, inthe form of a sleeve 'I0 is tightly mounted upon the sleeve 56 andextends downwardly for positive engagement with the lower portion of thecup 63, thereby protecting the fuse link against the cooling action ofthe surrounding medium and preventing the dissipation of heat away fromthe solder joint, which heat may be generated by the heater coil. It maybe noted that the conducting member 55 is of a lesser current-carryingcapacity than the heater coil 65 for reasons hereinafter' explained.

Integrally secured to the bottom or" the cup 63 is a downwardlyextending arm il to which a connector or clip 12 is detachably securedby means of a bolt 13 and which in turn is firmly attached at its lowerend 14 to the upper end of a helical spring 15 and to a fiexibleconducting cable or leader 16.

The liquid fuse operates electrically to conduct a current under normalconditions by means of the contact 52, the bridge 54, the conductor 55.the heater coil 65, the arm 'i l, the clip l2 and 'the conductor 16, andthe heat generated by the coil 65 is insuiiicient to melt the alloy 64.When a moderate overload current exists in the circuit to which the fusemay be connected, sufficient heat is generated by the coil 65 anddissipated through the material 61 and sides of the cup 63 to melt thealloy 64, thereby allowing the spring 15 to withdraw the cup and heatercoil from the sleeve 56 and break the mechanically weak electrical jointon the loop 62. Under conditions of heavy short circuit the lessercurrent-carrying capacity member 55 operates as a fusible section andmelts permitting the spring 15 to draw the fuse link 51 away from theruptured member 55, thereby introducing a gap in the circuit.

It may be noted here that substantially all of the heat generated by theyheater coil I5 is ,conducted through the cementitious material 81 andthe cup 83 radially outwardly toward theV alloy 64 and held Within thisarea by theinsulating medium 10, thereby preventing unnecessary loss ofheat to the surrounding area and delay inthe melting of the alloy I4 andinterruption of current flow through the various conducting portions.

From the foregoing description, it may be noted that the objects of thisinvention have been accomplished by providing al fractional amperagefuse link having a fusible section vvcomprising a pair' of cooperatingportions heldin rigid relationship to each other by a relativelylow-melting point alloy and by providing a heat-producing,

current-conducting means which operatesl at a.

predetermined value of current to allow separa# tion of the cooperatingportions by melting the 1. A fuse link comprising a pair of conductors,V

an insulator connected to one of said conductors,

a strain section connected to said insulator andk including a meltablealloy, a strain wire mechanically and electrically connected tothe otherof said conductors and with said strain section by said meltable alloy,and an electrically-conductive heater portion adjacent said section andconnected electrically with said conductors, said strain wire beingreleased from said strain sec-A tion when said alloy is melted by heattransmitted from said conductive heater upon the occurrence of apredetermined current iiow through said link.

2. A fuse link comprising a pair of conducting portions, a destructiblesection holding one of said portions in position relative to the other,a heater element connected electrically with said portions,

and an insulating member disposed between saidl portions and adapted toallow complete current iiow through said heater element, said elementacting when an overload current is established therethrough to producesuicient heat to destroy said section and interrupt the now of currentthrough said link.

3. A fuse link comprising a pair of conducting portions, a mechanicalconnection between said portions connected to one of said portions inelectrically non-conducting relationship thereto, a meltable alloysecuring the other of said portions to said connection, and apredetermined length of resistance wire connected electrically with saidportions and having a greater part of its length disposed in closeproximity to the alloy, said wire acting to-produce suiiicient heat tomelt said other of said alloy and allow separation of said other of saidportions and said connection, thereby introducing a gap in a circuitincluding the' link. A

4. A fuse link comprising a pair of conducting portions, a mechanicalconnection between said portions connected to one of said portions inelectrically non-conducting relationship thereto, a heat-responsivealloy securing the other of said portions to said connection, and apredetermined length of resistance wire connected electrically with saidportions and having a greater part of its length electrically insulatedfrom and disposed in close proximity to the alloy, said wire portions,an insulating l .upon one of said portions `and held` under tenfbridginlitheow of current around-,said alloyy and acting to producesumcient Vheat te melt said al-. Y

loy andI allow separation of said lothero! said portions and saidconnection, .thereby introducing a gap in a circuit including the link.e

5. Aiuse'link comprising apair of conducting tube, a 'spring mountedsion by said tube, a holding'means connecting said 'portions inelectrically non-conducting relation, a meltable"alloyv securing one 'ofsaid 'pori vtions to said means andan electrically-conductive heatersection surrounding .said holding means and connected electrically withsaid portions,`f"said heater section acting' to generate sumcient heatto-melt said'alloy and allow separation of `one of said portions fromsaidfalloy when `a vpredetermined currentl occurs in said link.

6; Atensioned fuse link comprising a terminal member, anV insulatingsleeve secured to said te'rminal member, a heat-conductive portionsecured to said sleeve vin electrically non-conducting relation to saidterminal member, a strain wire se-r cured to said conductive portionAbymeans of a meltable alloy, a conductor mechanically connected to saidstrain wire,4` and a predetermined length of resistance wire having agreater part of its length mountedon said heat-conductive portion andelectrically connecting said strain wire with said terminal, saidresistance wire acting `as an electrical conductor and a heat-producingagent, whereby sufficient heat is produced to melt said alloy when apredetermined value of current is established in said link, therebyallowing separation of said strain wire from said portion andinterrupting the flow of current therethrough.

'7. A tensioned fuse link comprising a terminal member, a first strainwire secured .to said terminal member, a holding means secured to saidwire by means of a predetermined melting point alloy, a second strainwire securedin insulated relation to said holding means, a conductormechanically connected to said second strain wire, and a' predeterminedlength of elec-- a meltable alloy carried by said metal strip, saidconducting portions held in iixed relation to each other by saidmeltable alloy, an electrically-conductive heater portion surroundingsaid metal strip and electrically connecting said conductive portion, aspring carried by one of said conductive portions, an insulating elementdisposed between said portions and adapted to permit c'urrent nowthrough said heater portion only, and a tube surrounding said sectionand lholding said spring under tension, whereby upon melting of saidmeltable alloy, a gap is introduced in a circuit including the link.

9. A fuse link comprising a pair of conducting portions, a strainsection connecting said portions and including a meltable alloy, astrain wire mechanically connected to one of said conducting portionsand held in electrical relation with said strain section by saidmeltable alloy, an electrically-conductive heater portion surroundingsaid section and electrically connecting said conductive portions, saidstrain wire having a lesser current-carrying capacity than said heaterportion thereby providing a fusible section for said link when said linkis subjected to heavy current flow.

10. A fuse link comprising a pair of conducting portions, a destructiblesection connecting said portions and including a meltable alloy, astrain wire mechanically connected to one of said conducting portionsand held in electrical relation with said strain section by saidmeltable alloy, an electrically-conductive heater portion surroundingsaid section and electrically connecting said conductive portions, saidstrain wire having a lesser current-carrying capacity than said heaterportion thereby providing a fusible section for said link when said linkis subjected to heavy current flow.

11. A disconnect device for electric circuits, said device including atubular member having an aperture extending through the side andadjacent one end thereof, a meltable alloy in said member, a conductorwire held by said meltable alloy, and a second wire extending into saidmember and outwardly through said aperture and then coiled about theouter periphery of said member.

12. A fuse link comprising a pair of spaced contacts, a heatdestructible section connecting said contacts and including a pair oftubular portions received in telescopic relation to each other, ameltable alloy normally holding said portions in fixed relation to eachother, and an electrically-conductive heater unit carried by one of saidtubular portions and electrically connecting said contacts, said alloybeing fused by said heater unit upon occurrence of an overload in saidlink.

13. A fuse link comprising a pair of conducting portions, a destructiblesection connecting said portions, said section including a tubularportion open at one end, a sleeve received in telescopic relation withsaid tubular portion, a meltable alloy normally holding said sleeve iniixed relation to said tubular portion, and an electrically conductiveheater unit carried in said tubular portion and electrically connectingsaid conducting portions, said alloy being fused by said heater unitupon occurrence of an overload in said link.

14. A fuse linkcom'prising a pair of conductlng portions, a strainsection connecting said contacts, said strain section including atubular portion open at one end, a sleeve received in telescopicrelation with said tubular portion, an

insulating element secured to one of said conducting portions and saidsleeve, a meltable alloy holding said sleeve in fixed relation to saidtubular portion, and an electrically-conductive heater unit carried insaid tubular portion and electrically-connecting said conductingportions, said alloy being fused by said heater unit upon occurance ofan overload in said link.

15. A fuse link comprising a pair of conducting portions, a strainsection connecting said contacts, said strain section including atubular portion open at one end, a sleeve received in telescopicrelation with said tubular portion, an insulating element secured to oneof said conducting portions and said sleeve, a meltable alloy holdingsaid sleeve in iixed relation to said tubular portion, an insulatingelement surrounding said sleeve, and an electrically-conductive heaterunit carried in said tubular portion and electrically-connecting saidconducting portions, said alloy being fused by said heater unit uponoccurrence of an overload in said link.

16. A fuse link comprising a rigid metal cony tact, an insulating tubehaving one end threaded on one end of said contact, a metal tubethreaded on the end of said insulating tube remote from said contact andhaving an aperture adjacent the end of said insulating tube, a strainwire extending into said metal tube and secured therein by means of alow melting alloy to normally prevent withdrawal of the wire therefrom,a conductor secured to said wire remote from said metal tube, and aninsulated conducting wire in said insulating tube electrically connectedto said metal contact and extending through the aperture in said metaltube andy being coiled about said metal tube, said insulated conductingwire being electrically connected with said strain wire at a poin'tremote from said insulating tube, whereby said metal tube iselectrically non-conducting and subjected to heat generated in thecoiled portion of said insulated conducting wire.

17. A fuse link comprising a terminal contact including a conductingportion, an insulating member supported by said conducting portion, atubular element supported by and in spaced relation to said insulatingmember, a conductor releasibly secured to said tubular element by meansof a low melting alloy, and a heater element concentrically positionedrelative to said tubular element adjacent said alloy, said heaterelement including a coiled insulated conducting wire electricallyconnected with said conducting portion and with said conductor at apoint remote from said insulating member.

RALPH H. EARLE.

Certificate of Correction Patent N o. 2,281,029 April 28, 1942 RALPH H.EARLE It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows:

Page 4, first column, line 62, strike out the Words "other of said; andthat the said Letters Patent should be read With this correction thereinthat the same may conform to the record of the case in the PatentOffice. Signed and sealed this 10th day of January, A. D. 1950.

[WAL] THOMAS F. MURPHY,

Assistant Uommssz'oner of Patents.

Certificate of Correction Paf-,ent No. 2,281,029 April 28, 1942 RALPH H.EARLE It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows:

Page 4, rst column, line 62, strike out the Words other of said and thatthe said Letters Patent should be read With this correction therein thatthe same may conform to the record of the ease in the Patent Office.Signed and sealed this 10th day of January, A. D. 1950.

[IML] THOMAS F. MURPHY,

Assistant Uommsstoner of Patents.

